It all began in a junkyard as they say. The first part of the serial opens on a foggy London night, and a patrolman checks the gate at I.M. Foreman Scrap Merchants, 76 Totter’s Lane. He walks away, and the gate opens and the camera enters the yard and settles on a police box as we hear a distinct humming noise. Fade to Coal Hill School, where two teachers, Barbara Wright and Ian Chesterton are talking about a student named Susan Foreman. They are bothered by the fact that she seems absolutely brilliant, but astoundingly dull in other ways. Barbara had tried to visit her grandfather, a “doctor,” but found that the address on file with the school office was the junkyard at 76 Totter’s Lane. They decide to follow her home and try to solve the mystery that is Susan Foreman. The teachers leave Susan and she picks up the book and immediately upon starting to read exclaims “that’s not right!”
The teachers watch her entering the junk yard and follow her in. They discover the police box, and soon encounter an old man. They hear Susan‘s voice inside the police box and argue with the old man about it, thinking he knows something about it. Susan opens the door and Barbara and Ian force their way in, discovering that they are not inside a police box, but a very large, complex machine with Susan inside.
The old man instructs Susan to close the door, and Ian argues with the old man about wanting an explanation how a police box can contain a vast room such as the one they are in. Susan calls the ship they are in the TARDIS, which stands for Time And Relative Dimensions In Space. The old man tells them that he and Susan are exiles, cut off from their own planet without friends or protection. He talks of them being wanderers in the fourth dimension of time. Ian tries to leave and gets shocked by the console. The old man and Susan argue about letting them go, and Susan tells him that if he tries to leave, she will leave him and the TARDIS. He activates the controls and the TARDIS takes off and lands in a rocky wilderness area. The first part of the story ends with a shadow looming menacingly near the TARDIS.
The second part opens with the same exterior scene of the TARDIS and the menacing shadow. The shadow is cast by a cave man who looks at the TARDIS in disbelief. The scene switches to a tribe of cave men where one of them, Za, is trying to make fire while being ridiculed by an old woman. Za and a woman talks about who will be leader of the tribe and whom her father will give her to. The scene switches to inside the TARDIS, where Barbara and Ian regain consciousness after having been knocked unconscious by the TARDIS’s trip.
Ian argues with the old man, calling him “Doctor Foreman,” to which the old man replies “doctor who?” They talk about the ship having gone back in time, but Ian is skeptical. They all exit the TARDIS, and Ian is dumbfounded, and the old man is wondering why the TARDIS still looks like a police box. Everyone starts exploring, Ian, Barbara and Susan exploring separating from the old man. Barbara refers to him as Doctor Foreman and Ian says “That’s not his name, who is he? Doctor Who?” The Doctor lights his pipe, and is attacked by a caveman named Kal who thinks that the Doctor can show him the secret of fire allowing Kal to take over the tribe. Susan, Barbara and Ian go to his aid and find that he has been taken. They take off in search of him as the scene shifts to the cave.
Za is having a hard time keeping his position as leader in the face of a challenge from Kal, and as Kal returns to the cave carrying the Doctor. Kal convinces the tribe that if he can bring them the secret of fire, that he should be leader. The Doctor awakens and tells the tribe that he would make fire for them, but he can’t make fire without matches. This adds to the conflict between Kal and Za. Kal threatens to kill the Doctor, but is interrupted by Susan, Ian and Barbara. They are overpowered by the tribe and imprisoned in the cave of skulls. Za and the woman’s father discuss her being mated with Za. As the second part ends, the four travelers discover that the cave gets its name from being littered with skeletons and skulls and that the skulls have all been split open.
In the main cave, an old woman of the tribe departs while the others are sleeping. In the cave of skulls, the travelers use a sharp edged stone to try to cut their bonds, and the Doctor tells them to use a sharp piece of bone. The old woman leaves the main cave and is seen by the woman, Hur, who wakes Za and they follow the old woman. The old woman comes into the cave of skulls, and tells the travelers they will not make fire. Hur tells Za that the old woman went to kill the travelers, and they go to follow her, overhearing her telling them that she will she them free if they do not make fire. The old woman frees them, and they escape through a back entrance to the cave of skulls.
The travelers escape into the forest at night and are pursued by Za. The travelers stop to catch their breath and Barbara is startled when she trips over a fresh corpse of an animal. They are being stalked by a wild animal, but they are saved by Za, who kills the animal, but is gravely wounded in the fight. Barbara goes to help the wounded Za, followed by Susan. Hur resists their help, and Ian tells them he is their friend and wants to treat his wounds. They argue over helping Za, and they make a stretcher to carry Za. Kal goes to the cave of skulls and questions the old woman, and Kal kills her.
While building the stretcher, the Doctor picks up a rock, and is stopped from killing Za by Ian. They begin to carry Za back to the TARDIS. Kal wakes the rest of the tribe and leads them out to stop the travelers, blocking hem from reaching the TARDIS as the third installment ends.
The final installment of this first serial starts with the travelers being taken prisoner once again. In the cave, an argument breaks out over who killed the old woman, Kal accusing Za. The Doctor tricks Kal into showing the tribe his bloody knife, forcing him to confess. The Doctor and Ian provoke the tribe to drive Kal out, and they are once again imprisoned in the cave of skulls for their trouble. They make fire for the tribe believing this to be their ticket to freedom, and give the fire to Za. Za is attacked by Kal, and in the fight, Za kills him. They ask to be set free now that they have given Za fire, but Za keeps them prisoner, forcing them to remain and join the tribe.
As the tribe celebrates the return of fire, the travelers use the fire to trick the tribe into believing that they are dead and escape. The tribe follows when they discover the deception and give chase, but the travelers reach the TARDIS and escape as spears are thrown at the vanishing TARDIS.